Suspension controlling apparatus for vehicle

ABSTRACT

In a suspension controlling apparatus for a vehicle which includes a suspension with a damping force that is variably settable and a control unit for controlling the damping force of the suspension on the basis of target damping force, the damping force of the suspension is controlled in response to stabilize the posture of a vehicle body even when a sudden acceleration variation occurs. A rotational speed difference across a clutch provided between an engine and a transmission is detected by the rotational speed difference detection member. A control unit changes target damping force to a given value when the rotational speed difference exceeds a first threshold value.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 USC 119 to JapanesePatent Application No. 2015-055849 filed Mar. 19, 2015 the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a suspension controlling apparatus fora vehicle which includes a suspension with a damping force that isvariably settable. A control unit is provided for controlling thedamping force of the suspension on the basis of target damping force.

2. Description of Background Art

A suspension controlling apparatus is known such that acceleration of avehicle in a forward and rearward direction is detected by anacceleration sensor and the damping force of a suspension is controlledon the basis of a detection value of the acceleration sensor. See, forexample, Japanese Patent Laid-Open No. 2010-184512.

However, in the suspension controlling apparatus disclosed in JapanesePatent Laid-Open No. 2010-184512, since it controls after a behavioroccurs on a vehicle body, if a sudden acceleration variation occurs uponstarting of the vehicle, upon engine braking or the like, the controlsometimes fails to follow up the variation. In this regard, animprovement with respect to the suspension controlling apparatus isdemanded.

SUMMARY AND OBJECTS OF THE INVENTION

The present invention has been made in view of such a situation asdescribed above. It is an object of an embodiment of the presentinvention to provide a suspension controlling apparatus for a vehicle bywhich, even when a sudden acceleration variation occurs, the dampingforce of a suspension can be controlled in a good response to stabilizethe posture of the vehicle body.

In order to achieve the above object, according to an embodiment of thepresent invention, a suspension controlling apparatus for a vehicleincludes a suspension whose damping force is variably settable. Acontrol unit is configured to control the damping force of thesuspension on the basis of a target damping force. The control unitincludes a rotational speed difference detection means for detecting arotational speed difference across a clutch provided between an engineand a transmission, the control unit changing the target damping forceto a given value when the rotational speed difference exceeds a firstthreshold value.

According to an embodiment of the present invention, the control unitcancels a state in which the target damping force is changed to thegiven value in response to a decrease in the rotational speed differenceto a level equal to or lower than a second threshold value which islower than the first threshold value.

According to an embodiment of the present invention, the suspensioncontrolling apparatus for a vehicle may further includes a stroke sensorconfigured to detect a stroke of the suspension, wherein the controlunit decides the vibration state from a detection value of the strokesensor.

According to an embodiment of the present invention, when the rotationalspeed on the engine side with respect to the clutch is equal to orhigher than the rotational speed on the transmission side with respectto the clutch, the control unit changes the first threshold value to athreshold value suitable for the starting of the vehicle and changes thegiven value to a given value suitable for the starting of the vehicle.

According to an embodiment of the present invention, when the rotationalspeed on the engine side with respect to the clutch is lower than therotational speed on the transmission side with respect to the clutch,the control unit changes the first threshold value to a threshold valuesuitable for engine braking and changes the given value to a given valuesuitable for engine braking.

According to an embodiment of the present invention, it is possible toperceive in advance that a sudden acceleration variation is caused bythe rotational speed difference across the clutch between the engine andthe transmission and control the damping force of the suspensionappropriately in advance. Consequently, the posture of the vehicle bodycan be stabilized.

According to an embodiment of the present invention, the ordinary targetvalue control can be restored in response to a decrease of therotational speed difference across the clutch.

According to an embodiment of the present invention, the damping forceof the suspension can be controlled appropriately in response to thegear ratio of the transmission.

According to an embodiment of the present invention, upon starting ofthe vehicle, the damping force of the suspension can be set to anappropriate level.

According to an embodiment of the present invention, upon enginebraking, the damping force of the suspension can be set to anappropriate level.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a block diagram depicting a configuration of a driving systemof a motorcycle;

FIG. 2 is a block diagram depicting a configuration of a suspensioncontrolling apparatus;

FIG. 3 is a block diagram depicting a portion of a control unit whichcontrols a suspension for a front wheel;

FIG. 4 is a block diagram depicting a configuration of a selection unit;

FIG. 5 is a block diagram depicting a configuration of a pitchcontrolling target damping force calculation unit;

FIG. 6 is a timing chart illustrating a variation caused by a suddenthrottle operation upon execution of pitch suppression control;

FIG. 7 is a block diagram depicting a configuration of a skyhookcontrolling target damping force calculation unit;

FIG. 8 is a view depicting a variation of skyhook controlling targetdamping force in response to a roll angle; and

FIG. 9 is a timing chart upon execution of skyhook control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, an embodiment of the present invention is describedwith reference to FIGS. 1 to 9. Referring first to FIG. 1, rotationalpower of a crankshaft 11 provided on an engine mounted on a vehicle suchas a motorcycle is transmitted to an input member 12 a of a clutch 12through a primary reduction gear mechanism 13. The power from an outputmember 12 b of the clutch 12 is inputted to a transmission 14. Thetransmission 14 is configured from selectively engageable first to sixthspeed gear trains provided, for example, between a main shaft 15 and acountershaft 16. In a neutral state of the transmission 14, therotational power transmitted from the output member 12 b of the clutch12 to the main shaft 15 is not transmitted to the countershaft 16.However, when the transmission 14 is not in the neutral state, therotational power is transmitted to the countershaft 16 at a gear ratiogiven by selective engagement of the first to sixth speed gear trains.The rotational power of the countershaft 16 is transmitted to a rearwheel WR serving as a driving wheel through a final reduction gearmechanism 17.

As a rotational speed of the engine side with respect to the clutch 12,the rotational speed of the engine, namely, the rotational speed of thecrankshaft 11 is detected by an engine speed sensor 18. Meanwhile, as arotational speed of the transmission 14 side with respect to the clutch12, the rotational speed of the countershaft 16 is detected by acountershaft rotational speed sensor 19. The gear ratio of thetransmission 14 is decided by gear ratio decision means 20 for detectingthe rotational angle of a shift drum provided in the transmission 14.

Referring to FIG. 2, a front wheel WF is suspended at a front portion ofa vehicle body B of the motorcycle through a suspension 22F for a frontwheel having a solenoid 21F by which damping force can be variably set.The rear wheel WR is suspended at a rear portion of the vehicle body Bthrough a suspension 22R for a rear wheel having a solenoid 21R by whichthe damping force can be variably set.

A hydraulic brake is provided for the front wheel WF. Braking operationof the hydraulic brake is controlled by a brake system 23 which cancarry out also antilock braking control. Output hydraulic pressure of amaster cylinder (not depicted), provided in the brake system 23, isdetected by a hydraulic pressure sensor 24 and represents a brakeoperation amount. A stroke sensor 25F for detecting a stroke of thesuspension 22F for the front wheel is provided between the vehicle bodyB and the front wheel WF. A stroke sensor 25R for detecting a stroke ofthe suspension 22R for the rear wheel is provided between the vehiclebody B and the rear wheel WR. Further, a vertical acceleration sensor26F for detecting a vertical acceleration of a front portion of thevehicle body B by the suspension 22F for the front wheel and a verticalacceleration sensor 26R for detecting a vertical acceleration of a rearportion of the vehicle body B by the suspension 22R for the rear wheelare provided on the vehicle body B.

The damping force of the suspensions 22F and 22R varies by control ofthe operation of the solenoids 21F and 21R by a control unit 28. Thecontrol unit 28 receives signals inputted thereto from the engine speedsensor 18, countershaft rotational speed sensor 19, gear ratio decisionmeans 20, hydraulic pressure sensor 24, stroke sensors 25F and 25R andvertical acceleration sensors 26F and 26R. Also signals from a rollangle sensor 29 for detecting a roll angle of the motorcycle, a vehiclespeed sensor 30 for detecting the vehicle speed, a throttle sensor 31and an actual acceleration sensor 32 for detecting an actualacceleration in the forward and rearward direction of the vehicle areinputted to the control unit 28. The throttle sensor 31 may be anysensor if it detects the opening of a throttle valve of the engine, anoperation amount of a throttle grip and an intake air negative pressureof the engine. Further, a signal indicative of whether or not antilockbraking control is being executed is inputted from the brake system 23to the control unit 28.

Referring to FIG. 3, the control unit 28 includes a skyhook controllingdamping force calculation unit 34, a pitch suppression controllingdamping force calculation unit 35, a base damping force calculation unit36, high select means 37, starting-engine brake damping force settingmeans 38, a target current calculation unit 41, changeover means 39, anda selection unit 40. The skyhook controlling damping force calculationunit 34 determines damping force for skyhook control of the suspensions22F and 22R so as to stabilize the vehicle body against a road surfaceinput. The pitch suppression controlling damping force calculation unit35 determines damping force for pitch suppression control by which thesuspensions 22F and 22R are controlled so that an appropriate pitchbehavior in response to an operation input of a vehicle rider may beobtained. The base damping force calculation unit 36 determines dampingforce as a reference upon normal traveling in which none of the skyhookcontrol and the pitch suppression control is executed. The high selectmeans 37 selects a maximum one of values of the damping force determinedby the skyhook controlling damping force calculation unit 34, pitchsuppression controlling damping force calculation unit 35 and basedamping force calculation unit 36. The starting-engine brake dampingforce setting means 38 determines damping force for vehicle starting andfor engine braking. The target current calculation unit 41 calculatestarget current in response to the damping force inputted on the basis ofthe characteristics of the suspensions 22F and 22R. The changeover means39 carries out changeover between a state in which an output of the highselect means 37 is inputted to the target current calculation unit 41and another state in which an output of the starting-engine brakedamping force setting means 38 is inputted to the target currentcalculation unit 41. The selection unit 40 selects one of the states tobe assumed by the changeover means 39.

To the starting-engine brake damping force setting means 38, a detectionvalue of the engine speed sensor 18 which detects the rotational speedof the engine as the rotational speed of the engine side with respect tothe clutch 12, a detection value of the countershaft rotational speedsensor 19 which detects the rotational speed of the countershaft 16 anda gear ratio decided by the gear ratio decision means 20 are inputted.The starting-engine brake damping force setting means 38 calculates therotational speed of the main shaft 15 which is the rotational speed ofthe transmission 14 side with respect to the clutch 12 from the gearratio decided by the gear ratio decision means 20 and the rotationalspeed of the countershaft 16 detected by the countershaft rotationalspeed sensor 19. When the rotational speed of the engine side withrespect to the clutch 12 is equal to or higher than the rotational speedof the transmission 14 side with respect to the clutch 12, thestarting-engine brake damping force setting means 38 sets the dampingforce to a given value suitable for starting of the vehicle. However,when the rotational speed of the engine side with respect to the clutch12 is lower than the rotational speed of the transmission 14 side withrespect to the clutch 12, the starting-engine brake damping forcesetting means 38 sets the damping force to a given value suitable forengine braking.

Referring to FIG. 4, the selection unit 40 includes rotational speeddifference detection means 42, comparison means 43, first thresholdvalue setting means 44 and second threshold value setting means 45. Therotational speed difference detection means 42 calculates the rotationalspeed difference across the clutch 12 provided between the engine andthe transmission 14 on the basis of detection values of the engine speedsensor 18, countershaft rotational speed sensor 19 and gear ratiodecision means 20. The comparison means 43 inputs, to the changeovermeans 39, a signal for determining to which state the changeover means39 is to be set on the basis of the rotational speed difference obtainedby the rotational speed difference detection means 42.

The rotational speed difference detection means 42 detects therotational speed difference across the clutch 12 from the rotationalspeed of the engine, namely, of the crankshaft 11, detected by theengine speed sensor 18 and the rotational speed of the main shaft 15calculated on the basis of the detection values of the countershaftrotational speed sensor 19 and the gear ratio decision means 20.

The comparison means 43 receives, as inputs thereto, a first thresholdvalue determined by the first threshold value setting means 44 and asecond threshold value determined by the second threshold value settingmeans 45. When the rotational speed difference exceeds the firstthreshold value, the comparison means 43 inputs, to the changeover means39, a signal for inputting the given value determined by thestarting-engine brake damping force setting means 38 to the targetcurrent calculation unit 41. However, the comparison means 43 inputs, tothe changeover means 39, a signal for inputting the target damping forceoutputted from the high select means 37 to the target currentcalculation unit 41 in response to a drop of the rotational speeddifference to a level equal to or lower than the second threshold value.

To the first threshold value setting means 44, a detection value of theengine speed sensor 18, a detection value of the countershaft rotationalspeed sensor 19 and a gear ratio decided by the gear ratio decisionmeans 20 are inputted. When the detection value of the engine speedsensor 18 is equal to or higher than the rotational speed of the mainshaft 15 obtained on the basis of the detection values of thecountershaft rotational speed sensor 19 and the gear ratio decisionmeans 20, the first threshold value setting means 44 sets the firstthreshold value to a threshold value which is suitable for starting ofthe vehicle and varies in response to the gear ratio. However, when thedetection value of the engine speed sensor 18 is lower than therotational speed of the main shaft 15, the first threshold value settingmeans 44 sets the first threshold value to a threshold value which issuitable for engine braking and varies in response to the gear ratio.The second threshold value setting means 45 determines the secondthreshold value as a value lower than the first threshold value.

According to such a configuration of the changeover means 39 and theselection unit 40 as described above, when the rotational speeddifference across the clutch 12 detected by the rotational speeddifference detection means 42 exceeds the first threshold value, thetarget damping force determined by one of the skyhook controllingdamping force calculation unit 34, pitch suppression controlling dampingforce calculation unit 35 and base damping force calculation unit 36 ischanged to the given value. Further, in response to a drop of therotational speed difference to a level equal to or lower than the secondthreshold value which is lower than the first threshold value, the statein which the target value is changed to the given value is canceled. Inaddition, the first threshold value changes in response to the gearratio of the transmission 14, and when the rotational speed of theengine side with respect to the clutch 12 is equal to or higher than therotational speed of the transmission 14 side with respect to the clutch12, the first threshold value is set to a threshold value suitable forstarting of the vehicle. However, when the rotational speed of theengine side with respect to the clutch 12 is lower than the rotationalspeed of the transmission 14 side with respect to the clutch 12, thefirst threshold value is set to a threshold value suitable for enginebraking. It is to be noted that the given value described above may varyin response to the rotational speed difference higher than the firstthreshold value.

To the base damping force calculation unit 36 which determines dampingforce to be used as a reference upon ordinary travelling in which noneof skyhook control and pitch suppression control is executed, thedetection values of the roll angle sensor 29 and the vehicle speedsensor 30 are inputted. The base damping force calculation unit 36determines damping force to be used as a reference upon ordinarytraveling on the basis of a map determined in advance which correspondsto the roll angle and the vehicle speed.

Referring to FIG. 5, the pitch suppression controlling damping forcecalculation unit 35 includes acceleration calculation means 45A andtarget damping force setting means 47. The acceleration calculationmeans 45A calculates a forward and rearward direction acceleration ofthe vehicle on the basis of an operation input amount to the vehicle.The target damping force setting means 47 determines target dampingforce for pitch suppression control by a map search on the basis of theforward and rearward direction acceleration of the vehicle and adifferentiation value of the acceleration.

The operation input amount to the vehicle is a throttle operation amountobtained by the throttle sensor 31 and a hydraulic pressure obtained bythe hydraulic pressure sensor 24. Engine torque calculation means 48calculates engine torque on the basis of the engine speed obtained bythe engine speed sensor 18 and the throttle operation amount. Drivingforce calculation means 49 calculates driving force on the basis of thegear ratio obtained by the gear ratio decision means 20 and the enginetorque. The driving force and a traveling resistance obtained bytraveling resistance calculation means 50 are inputted to theacceleration calculation means 45A. The traveling resistance calculationmeans 50 calculates standard traveling resistance on the basis of thevehicle speed obtained by the vehicle speed sensor 30.

Ordinary braking force estimation means 51 estimates ordinary brakingforce on the basis of the hydraulic pressure obtained by the hydraulicpressure sensor 24, and upon ordinary braking in which antilock brakingcontrol is not executed, the ordinary braking force estimated by theordinary braking force estimation means 51 is inputted to theacceleration calculation means 45A. On the other hand, braking force forantilock braking control when the signal from the brake system 23indicates an antilock braking controlling state is estimated by the ABSbraking force estimation means 52 on the basis of fixed deceleratingforce and a detection value of the actual acceleration sensor 32.

The braking forces estimated by the ordinary braking force estimationmeans 51 and the ABS braking force estimation means 52 are changed overby changeover means 53 in response to a braking state obtained from thebrake system 23 and are inputted to the acceleration calculation means45A. In particular, upon ordinary braking, the ordinary braking forceestimated by the ordinary braking force estimation means 51 is inputtedto the acceleration calculation means 45A whereas, upon antilock brakingcontrol, the given braking force for antilock braking control estimatedby the ABS braking force estimation means 52 is inputted to theacceleration calculation means 45A.

The acceleration calculation means 45A receives driving force, standardtraveling resistance and braking force inputted thereto and calculatesacceleration in the forward and rearward direction on the basis of theacceleration force and the deceleration force applied to the motorcycle.

The acceleration in the forward and rearward direction obtained by theacceleration calculation means 45A is inputted to selection means 54.The selection means 54 selects the actual acceleration obtained by theactual acceleration sensor 32 when the acceleration in the forward andrearward direction obtained by the acceleration calculation means 45Awhen the braking state obtained from the brake system 23 is an antilockbraking controlling state is equal to or lower than a givenacceleration. However, in any other case, the selection means 54 selectsthe acceleration in the forward and rearward direction obtained by theacceleration calculation means 45A. The acceleration outputted from theselection means 54 is inputted to the target damping force setting means47 and inputted also to first differentiation means 46. The accelerationis differentiated by the first differentiation means 46, and adifferentiation value of the acceleration obtained by thedifferentiation is inputted to the target damping force setting means47.

The target damping force determined by the target damping force settingmeans 47 is inputted to variation amount limit processing means 55. Tothe variation amount limit processing means 55, also a variation amountlimit value for limiting the variation amount of the target dampingforce for the suspensions 22F and 22R is inputted. The variation amountlimit processing means 55 carries out a limiting process for limitingthe variation amount of the target damping force determined by thetarget damping force setting means 47 so that the variation amount doesnot to exceed the variation amount limit value. In particular, the givenacceleration variation amount limit value obtained by accelerationvariation amount limit value setting means 56 as the variation amountlimit value upon acceleration and the given deceleration variationamount limit value obtained by deceleration variation amount limit valuesetting means 57 as a variation amount limit value upon deceleration arechanged over by changeover means 58 on the basis of the signal outputtedfrom the selection means 54 and inputted to the variation amount limitprocessing means 55. The target damping force for pitch suppressioncontrol obtained by the limiting process by the variation amount limitprocessing means 55 is outputted from the pitch suppression controllingdamping force calculation unit 35.

According to such pitch suppression control, for example, if a ridercarries out a sudden throttle operation, then the target damping forcefor pitch suppression control is changed to set target damping forcebefore a pitch behavior appears on the vehicle body as indicated by atiming chart of FIG. 6. In particular, driving force is estimated on thebasis of the throttle opening and the acceleration in the forward andrearward direction is estimated on the basis of the driving force, andthen target damping force is determined on the basis of the accelerationand a differentiation value of the acceleration. Therefore, if thethrottle opening increases suddenly at time t1, then the target dampingforce immediately changes in response to a variation of the estimateddriving force, acceleration in the forward and rearward direction anddifferentiation value of the acceleration. Thereupon, the target dampingforce changes so as to increase a time period ΔT (for example, 120milliseconds) prior to appearance of a pitch behavior on the vehiclebody. Further, if the throttle opening decreases suddenly at time t2,then the target damping force immediately changes in response to avariation of the estimated driving force, acceleration in the forwardand rearward direction and differentiation value of the acceleration.Thereupon, the change of the target damping force appears more than thetime period ΔT prior to the time at which the vehicle body pitch anglechanges to the decreasing side.

Referring to FIG. 7, the skyhook controlling damping force calculationunit 34 includes target damping force setting means 61 which determinestarget damping force for skyhook control on the basis of detectionvalues of the vertical acceleration sensor 26F, roll angle sensor 29 andvehicle speed sensor 30.

The vertical acceleration obtained by the vertical acceleration sensor26F is inputted to integration means 62 serving as vertical speeddetection means. The integration means 62 integrates the verticalacceleration to obtain a vertical speed, which is inputted to the targetdamping force setting means 61. Stroke amounts of the suspensions 22Fand 22R obtained by the stroke sensors 25F and 25R are inputted tosecond differentiation means 70, which differentiates the stroke amountsto obtain stroke speeds. The stroke speeds are inputted to the targetdamping force setting means 61. Further, detection values of the rollangle sensor 29 and the vehicle speed sensor 30 are inputted to skyhookcoefficient calculation means 63, and a skyhook coefficient whichdepends upon the roll angle and the vehicle speed is inputted to thetarget damping force setting means 61.

The target damping force setting means 61 arithmetically operates andsets target damping force from a sprung vertical speed obtained by theintegration means 62, an unsprung vertical speed determined from thestroke speed obtained by the second differentiation means 70 and theskyhook coefficient on the basis of the skyhook theory.

The skyhook controlling damping force calculation unit 34 includessuspension state detection means 71 for deciding whether the suspensions22F and 22R are in a compressed state or in a decompressed state, andtarget damping force limit value determination means 64 for determininga limit value to the target damping force.

The suspension state detection means 71 decides, from the sprungvertical speed obtained by the integration means 62 and the unsprungvertical speed determined from the stroke speed obtained by the seconddifferentiation means 70, which one of the compressed state and thedecompressed state is taken by each of the suspensions 22F and 22R.However, the decision may be made otherwise from the stroke amounts ofthe suspensions 22F and 22R obtained by the stroke sensors 25F and 25Ras indicated by a chain line in FIG. 7.

The target damping force limit value determination means 64 determines alimit value to the target damping force on the basis of a detectionvalue of the suspension state detection means 71 and a roll angleobtained by the roll angle sensor 29. In particular, the target dampingforce limit value determination means 64 determines a target dampingforce limit value on the compression side when the suspensions 22F and22R are in a compressed state and a target damping force limit value onthe decompression side when the suspensions 22F and 22R are in adecompressed state such that a value obtained by subtracting the targetdamping force limit value on the compression side from the targetdamping force limit value on the decompression side may increase as theroll angle increases as depicted in FIG. 8. In particular, the targetdamping force limit value on the compression side is set so as todecrease as the roll angle increases, and the target damping force limitvalue on the decompression side is set so as to increase as the rollangle increases. Thereupon, the target damping force limit value on thedecompression side may be higher than the target damping force limitvalue on the compression side irrespective of the roll angle asindicated by a solid line in FIG. 8, and in a region in which the rollangle is small, the target damping force limit value on the compressionside may be higher than the target damping force limit value on thedecompression side as indicated by a chain line in FIG. 8.

Further, as depicted in FIG. 7, a vehicle speed obtained by the vehiclespeed sensor 30 is inputted to the target damping force limit valuedetermination means 64. The target damping force limit valuedetermination means 64 changes the magnitude or the gradient of thetarget damping force limit value on the compression side and the targetdamping force limit value on the decompression side in response to thevehicle speed.

Meanwhile, a skyhook coefficient determined by the skyhook coefficientcalculation means 63 may be set such that the target damping force setby the target damping force setting means 61 decreases in a state inwhich the vehicle speed exceeds a given speed or may be set such that itis outputted as map data determined in advance depending upon the rollangle and the vehicle speed.

The skyhook controlling damping force calculation unit 34 has low selectmeans 65 which selects a lower value from between the target dampingforce determined by the target damping force setting means 61 and thetarget damping force limit value determined by the target damping forcelimit value determination means 64. In particular, if the target dampingforce for skyhook control determined by the target damping force settingmeans 61 exceeds the target damping force limit value determined by thetarget damping force limit value determination means 64, then the targetdamping force limit value is outputted as skyhook target damping forcefrom the low select means 65.

The target damping force for skyhook control outputted from the lowselect means 65 is outputted from execution decision means 66 only whenexcitation decision means 73 decides that a vibration state of thevehicle in the vertical direction is a given vibration state.

The excitation decision means 73 receives detection values of the strokesensors 25F and 25R filtered by a filter 68 and an excitation decisionthreshold value determined by excitation decision threshold valuedetermination means 69 as inputs thereto. The excitation decision means73 decides that a state in which the detection values of the strokesensors 25F and 25R exceed the excitation decision threshold value is agiven vibration state.

The excitation decision threshold value determination means 69 receives,as inputs thereto, target damping force calculated by the pitchsuppression controlling damping force calculation unit 35 and outputtedfrom the changeover means 39 and acceleration in the forward andrearward direction outputted from the selection means 54 of the pitchsuppression controlling damping force calculation unit 35. Theexcitation decision threshold value determination means 69 changes theexcitation decision threshold value to a value on a side on whichskyhook control is less likely to be started when the acceleration inthe forward and rearward direction is outside a given range. Further,during execution of pitch suppression control, the excitation decisionthreshold value determination means 69 changes the excitation decisionthreshold value to a value on the side on which skyhook control is lesslikely to be started. More specifically, when the acceleration in theforward and rearward direction is outside the given range and whilepitch suppression control is being executed, the excitation decisionthreshold value determination means 69 changes a decision condition forthe given vibration state for deciding whether or not skyhookcontrolling damping force control is to be started to a condition on theside on which skyhook control is less likely to be started.

According to such skyhook control, skyhook control is started at time t3at which the stroke detected by the stroke sensor 25F and filtered bythe filter 68 exceeds the excitation decision threshold value asdepicted in FIG. 9. Thus, damping force control of the suspension 22F isexecuted on the basis of the determined skyhook controlling targetdamping force.

While the damping force of the suspensions 22F and 22R is controlled bythe control unit 28 on the basis of target damping force, the controlunit 28 has the rotational speed difference detection means 42 fordetecting a rotational speed difference across the clutch 12 providedbetween the engine and the transmission 14 and changes the targetdamping force to a given value when the rotational speed differenceexceeds the first threshold value. Therefore, it is perceived in advancethat a sudden acceleration variation is caused by the rotational speeddifference across the clutch 12 between the engine and the transmission14, and the damping force of the suspensions 22F and 22R can becontrolled appropriately in advance. Consequently, the posture of thevehicle body can be stabilized.

Further, the control unit 28 cancels the state in which the targetdamping force is changed to the given value in response to a decrease ofthe rotational speed difference to a value equal to or lower than thesecond threshold value which is lower than the first threshold value.Therefore, the ordinary target damping force control can be restored inresponse to a decrease of the rotational speed difference across theclutch 12.

Further, since the control unit 28 changes the first threshold value inresponse to a decision result of the gear ratio decision means 20 fordeciding a gear ratio of the transmission 14, the damping force of thesuspensions 22F and 22R can be controlled appropriately in response tothe gear ratio of the transmission 14.

Further, the control unit 28 changes the first threshold value to athreshold value suitable for starting of the vehicle and changes thegiven value to a given value suitable for starting of the vehicle whenthe rotational speed on the engine side with respect to the clutch 12 isequal to or higher than the rotational speed on the transmission 14 sidewith respect to the clutch 12. Therefore, upon starting of the vehicle,the damping force of the suspensions 22F and 22R can be set to anappropriate level.

The control unit 28 changes the first threshold value to a thresholdvalue suitable for engine braking and changes the given value to a givenvalue suitable for engine braking when the rotational speed on theengine side with respect to the clutch 12 is lower than the rotationalspeed on the transmission 14 side with respect to the clutch 12.Therefore, upon engine braking, the damping force of the suspensions 22Fand 22R can be set to an appropriate level.

The control unit 28 includes the pitch suppression controlling dampingforce calculation unit 35 which determines damping force for pitchsuppression control in which the suspensions 22F and 22R are controlledso that an appropriate pitch behavior corresponding to an operationinput of the vehicle rider is obtained. The pitch suppressioncontrolling damping force calculation unit 35 has the accelerationcalculation means 45A and the target damping force setting means 47. Theacceleration calculation means 45A calculates acceleration in theforward and rearward direction of the vehicle on the basis of anoperation input amount to the vehicle. The target damping force settingmeans 47 determines target damping force for pitch suppression controlon the basis of a damping force map determined in advance in response tothe acceleration and a differentiation value of the acceleration. Thecontrol unit 28 thus calculates acceleration on the basis of anoperation input amount to the vehicle and determines target dampingforce of the suspensions 22F and 22R from the map on the basis of theacceleration and a differentiation value of the acceleration. Therefore,the suspensions 22F and 22R can react in a good response reading a willof the rider from the operation amount of the rider, and the dampingforce of the suspensions 22F and 22R can be controlled with a desirablecontrol amount prior to a behavior of the vehicle body.

The pitch suppression controlling damping force calculation unit 35includes the traveling resistance calculation means 50 which calculatestraveling resistance of the vehicle on the basis of the vehicle speeddetected by the vehicle speed sensor 30. Since the accelerationcalculation means 45A calculates acceleration in the forward andrearward direction of the vehicle on the basis of the travelingresistance obtained by the traveling resistance calculation means 50 andthe operation input amount, the acceleration calculation means 45Acalculates acceleration in the forward and rearward direction of thevehicle taking not only the operation input amount but also thetraveling resistance of the vehicle calculated on the basis of thevehicle speed into consideration. Consequently, acceleration of a higherdegree of accuracy can be obtained and more accurate suspension controlcan be achieved.

The driving force calculation means 49 calculates driving force on thebasis of the engine speed detected by the engine speed sensor 18 and thethrottle operation amount detected by the throttle sensor 31, and theacceleration calculation means 45A calculates acceleration on the basisof the driving force and the gear ratio of the transmission 14 decidedby the gear ratio decision means 20. Therefore, the acceleration iscalculated eliminating the necessity for a sensor for directly detectingacceleration of the vehicle in the forward and rearward direction, andthe suspensions can be controlled with a high response.

The acceleration calculation means 45A calculates acceleration on thebasis of deceleration corresponding to the detection value of thehydraulic pressure sensor 24 which detects the brake operation amount asthe operation input amount. Therefore, the deceleration is calculatedeliminating the necessity for a sensor for directly detectingacceleration of the vehicle in the forward and rearward direction, andthe suspensions 22F and 22R can be controlled with a high response.

In addition, since the acceleration calculation means 45A calculatesacceleration on the basis of the braking force and the driving force ofthe engine, the acceleration upon braking can be calculated with a highdegree of accuracy. Further, since the acceleration calculation means45A calculates the driving force of the engine on the basis of thetorque of the engine, the acceleration calculation means 45A cancalculate the driving force during braking with a high degree ofaccuracy and thus can calculate the acceleration during braking with ahigher degree of accuracy. Further, since the driving force of theengine is calculated on the basis of the torque of the engine and thegear ratio, the driving force during braking can be calculated with ahigh degree of accuracy, and the acceleration during braking can becalculated with a higher degree of accuracy.

Since the variation amount limit value is set in advance by the pitchsuppression controlling damping force calculation unit 35 such that thevariation amount of the target damping force is limited, an excessivelygreat variation of the damping force of the suspensions 22F and 22R canbe suppressed. For example, when a sudden damping force variation occursupon a change from sudden acceleration to steady acceleration, thedamping force can be made closer to the target damping force for everyvariation amount limit value. Therefore, the damping force can be variedsmoothly. In addition, since a variation amount limit value duringacceleration and a variation amount limit value during deceleration forlimiting the variation amount of the target damping force are set inadvance, the pitch suppression controlling damping force calculationunit 35 can suppress an excessively great variation of the damping forcewhile it can be appropriately made suitable for acceleration and fordeceleration.

Although the acceleration calculation means 45A calculates, uponordinary braking, acceleration on the basis of ordinary braking forcecorresponding to the detection value of the hydraulic pressure sensor24, upon antilock braking control, the acceleration calculation means45A calculates acceleration on the basis of given antilock brakecontrolling braking force. Therefore, also upon antilock brakingcontrol, appropriate suspension control can be carried out.

The pitch suppression controlling damping force calculation unit 35determines, when the acceleration calculated by the accelerationcalculation means 45A during antilock braking control is equal to orlower than the given acceleration, the target deceleration force isdetermined on the basis of the actual acceleration obtained by theactual acceleration sensor 32 which detects the actual acceleration ofthe vehicle in the forward and rearward direction. Therefore, even if adifference appears between the actual acceleration and the accelerationcalculated on the basis of the brake hydraulic pressure depending uponthe state of the road surface on which the vehicle travels, the dampingforce can be controlled appropriately using the actual acceleration.

The control unit 28 includes the skyhook controlling damping forcecalculation unit 34 which determines the damping force for skyhookcontrol of the suspensions 22F and 22R so as to stabilize the vehiclebody against a road surface input. The skyhook controlling damping forcecalculation unit 34 includes the target damping force setting means 61which arithmetically operates and sets target damping force from asprung vertical speed obtained by the integration means 62, an unsprungvertical speed determined from a stroke speed obtained by the seconddifferentiation means 70 and a skyhook coefficient on the basis of theskyhook theory. Therefore, the stability of the vehicle can be promotedfurther.

The skyhook controlling damping force calculation unit 34 includes thesuspension state detection means 71 for deciding whether the suspensions22F and 22R are in a compressed state or in a decompressed state, andthe target damping force limit value determination means 64 fordetermining a limit value to the target damping force. Moreparticularly, the target damping force limit value determination means64 determines the limit value to the target damping force such that avalue obtained by subtracting the target damping force limit value onthe compression side when the suspensions 22F and 22R are in acompressed state from the target damping force limit value on thedecompression side when the suspensions 22F and 22R are in adecompressed state increases as the roll angle of the vehicle obtainedby the roll angle sensor 29 increases whereas the target damping forcelimit value on the compression side decreases as the roll angleincreases. The low select means 65 selects a lower value from betweenthe target damping force determined by the target damping force settingmeans 61 and the target damping force limit value determined by thetarget damping force limit value determination means 64. Therefore, thetarget damping force for the skyhook control when the suspensions 22Fand 22R are in a compressed state during turning is weakened.Consequently, while a vibration suppression performance is assured, therolling stability against an input from the road surface can beincreased. In addition, a moderate pitching behavior is provided atrising from a corner. Consequently, a turning characteristic is improvedappropriate damping force can be obtained, and besides a response tosteering can be assured.

The skyhook controlling damping force calculation unit 34 determines,when the target damping force for skyhook control determined by thetarget damping force setting means 61 exceeds the damping force limitvalue, the damping force limit value as the target damping force forskyhook control. Therefore, the control amount for the suspensions 22Fand 22R can be suppressed to a value equal to or lower than the dampingforce limit value.

Since the damping force limit value changes in response to the verticalspeed and the roll angle, the control amount for the suspensions 22F and22R can be suppressed to a value equal to or lower than the dampingforce limit value in response to various vehicle states.

The excitation decision threshold value determination means 69 providedin the skyhook controlling damping force calculation unit 34 changes,when the acceleration in the forward and rearward direction is outsidethe given range and during execution of pitch suppression control, theexcitation decision threshold value so that the decision condition for agiven vibration state for deciding whether or not the skyhookcontrolling damping force control is to be started is set to a conditionon the side on which skyhook control is less likely to be started.Further, when the excitation decision means 73 decides that thevibration state of the vehicle in the vertical direction is in the givenvibration state on the basis of the excitation decision threshold value,the excitation decision threshold value determination means 69 outputstarget damping force for executing the skyhook control. Therefore, it ispossible to execute suspension control while a pitching behavior is leftappropriately. In addition, not turning on-off of skyhook control ischanged over directly, but ease of intervention is changed by changingthe threshold value. Therefore, upon occurrence of a disturbance forwhich vibration suppression is required, vibration suppression can bestarted appropriately.

Further, during execution of the pitch suppression control, the decisioncondition of the given vibration state is changed to a condition on theside on which damping force control for skyhook control of thesuspensions 22F and 22R is less likely to be started. Therefore, uponacceleration or deceleration or when pitching suppression control isbeing executed, excessive damping force control by the skyhook controlis not carried out.

The excitation decision means 73 decides the given vibration state whichis used as a reference for starting the skyhook control from the strokesof the suspensions 22F and 22R detected by the stroke sensors 25F and25R. Therefore, the vibration state of the vehicle can be detectedappropriately from the stroke amounts of the suspensions 22F and 22R.

While the embodiment of the present invention has been described, thepresent invention is not limited to the embodiment described above, butallows various design changes without departing from the spirit of thepresent invention described in the claims.

For example, the present invention can be applied not only to amotorcycle but also widely to vehicles including four-wheeled vehicles.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A suspension controlling apparatus for a vehicle, comprising: a suspension with a damping force that is variably settable; a controller for controlling the damping force of the suspension on the basis of a target damping force; and the controller including rotational speed difference detector, the rotational speed difference detector detecting a rotational speed difference between a clutch input member connected to an engine and a clutch output member, wherein the controller changes the target damping force to a given value when the rotational speed difference exceeds a first threshold value, wherein, at a time of starting the vehicle, when a rotational speed of the clutch input member is equal to or higher than a rotational speed of the clutch output member, the controller changes the first threshold value to a threshold value suitable for starting of the vehicle and changes the given value to a given value suitable for starting of the vehicle, and wherein, based on a throttle opening, the target dampening force is determined.
 2. The suspension controlling apparatus for a vehicle according to claim 1, wherein the controller cancels a state in which the target damping force is changed to the given value in response to a decrease of the rotational speed difference to a level equal to or lower than a second threshold value which is lower than the first threshold value.
 3. The suspension controlling apparatus for a vehicle according to claim 1, and further comprising: gear ratio detector for deciding a gear ratio of the transmission; wherein the controller changes the first threshold value in response to a result of the decision by the gear ratio detector.
 4. The suspension controlling apparatus for a vehicle according to claim 2, and further comprising: gear ratio detector for deciding a gear ratio of the transmission; wherein the controller changes the first threshold value in response to a result of the decision by the gear ratio detector.
 5. The suspension controlling apparatus for a vehicle according to claim 1, wherein, when the rotational speed of the clutch input member is lower than the rotational speed of the clutch output member, the controller changes the first threshold value to a threshold value suitable for engine braking and changes the given value to a given value suitable for engine braking.
 6. The suspension controlling apparatus for a vehicle according to claim 2, wherein, when the rotational speed of the clutch input member is lower than the rotational speed of the clutch output member, the controller changes the first threshold value to a threshold value suitable for engine braking and changes the given value to a given value suitable for engine braking.
 7. The suspension controlling apparatus for a vehicle according to claim 3, wherein, when the rotational speed of the clutch input member is lower than the rotational speed of the clutch output member, the controller changes the first threshold value to a threshold value suitable for engine braking and changes the given value to a given value suitable for engine braking.
 8. The suspension controlling apparatus for a vehicle according to claim 4, wherein, when the rotational speed of the clutch input member is lower than the rotational speed of the clutch output member, the controller changes the first threshold value to a threshold value suitable for engine braking and changes the given value to a given value suitable for engine braking.
 9. A suspension controlling apparatus for a vehicle, comprising: a suspension with a damping force that is variably settable; a rotational speed difference detector, the rotational speed difference detector detecting a rotational speed difference between a clutch input member connected to an engine and a clutch output member, and providing a signal based on the rotational speed difference; and a controller for receiving the signal from the rotational speed difference detector, said controller controlling the damping force of the suspension on the basis of a target damping force, wherein the controller changes the target damping force to a given value when the rotational speed difference exceeds a first threshold value, wherein, at a time of starting the vehicle, when a rotational speed of the clutch input member is equal to or higher than a rotational speed of the clutch output member, the controller changes the first threshold value to a threshold value suitable for starting of the vehicle and changes the given value to a given value suitable for starting of the vehicle, and wherein, based on a throttle opening, the target dampening force is determined.
 10. The suspension controlling apparatus for a vehicle according to claim 9, wherein the controller cancels a state in which the target damping force is changed to the given value in response to a decrease of the rotational speed difference to a level equal to or lower than a second threshold value which is lower than the first threshold value.
 11. The suspension controlling apparatus for a vehicle according to claim 9, and further comprising: gear ratio detector for deciding a gear ratio of the transmission; wherein the controller changes the first threshold value in response to a result of the decision by the gear ratio detector.
 12. The suspension controlling apparatus for a vehicle according to claim 10, and further comprising: gear ratio detector for deciding a gear ratio of the transmission; wherein the controller changes the first threshold value in response to a result of the decision by the gear ratio detector.
 13. The suspension controlling apparatus for a vehicle according to claim 9, wherein, when the rotational speed of the clutch input member is lower than the rotational speed of the clutch output member, the controller changes the first threshold value to a threshold value suitable for engine braking and changes the given value to a given value suitable for engine braking.
 14. The suspension controlling apparatus for a vehicle according to claim 10, wherein, when the rotational speed of the clutch input member is lower than the rotational speed of the clutch output member, the controller changes the first threshold value to a threshold value suitable for engine braking and changes the given value to a given value suitable for engine braking.
 15. A suspension controlling apparatus for a vehicle, comprising: a suspension with a damping force that is variably settable; a controller for controlling the damping force of the suspension on the basis of a target damping force; and the controller including rotational speed difference detector, the rotational speed difference detector detecting a rotational speed difference between a clutch input member connected to an engine and a clutch output member, the clutch output member configured to drive a main shaft of a transmission, wherein the controller changes the target damping force to a given value when the rotational speed difference exceeds a first threshold value, and wherein, when the rotational speed of the clutch input member is equal to or higher than the rotational speed of the clutch output member, the controller changes the first threshold value to a threshold value suitable for starting of the vehicle and changes the given value to a given value suitable for starting of the vehicle. 